110. Balanced Binary Tree

Given a binary tree, determine if it is height-balanced.

For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

代码如下：

 /**
  * Definition for a binary tree node.
  * public class TreeNode {
  *     int val;
  *     TreeNode left;
  *     TreeNode right;
  *     TreeNode(int x) { val = x; }
  * }
  */
 public class Solution {

     public boolean isBalanced(TreeNode root) {
       if(root==null)
       return true;

       if(DFS(root)==-1)
       return false;

       return true;

     }

     public int DFS(TreeNode root){
         int left=1,right=1;
         if(root.left!=null)
         {
             if(DFS(root.left)==-1)
             return -1;
             else
             left=left+DFS(root.left);
         }
         if(root.right!=null)
         {
             if(DFS(root.right)==-1)
             return -1;
             else
             right=right+DFS(root.right);
         }

         if(left-right<-1||left-right>1)
         return -1;

         return Math.max(left,right);
     }

 }